How to get banner_ad_unit_id from AdMob (Android App)?
Warning!
Do not click on your own ads and advertisements in your own application! Do not look Rewarded Ads in your own application!
You should use the following identifiers for testing (if you want to click on ads in your application) so that you are not banned:
For test Admob banner in you app you need use "banner_ad_unit_id":
ca-app-pub-3940256099942544/6300978111
For test Rewarded Ads in you app you need use "rewarded_ad_unit_id":
ca-app-pub-3940256099942544/5224354917
App Id for testing "admob_app_id":
ca-app-pub-3940256099942544~3347511713
After testing, and before publishing the application, enter your real IDs.
In their applications, we actively use AdMob. Here we decided to show you how easily and quickly perform Ad unit ID from AdMob. To get the Ad unit ID from AdMob you need only a few simple steps:
1.) Log in or sign up https://www.google.com/admob
2.) Click -> Apps, Click -> "ADD APP"

3.) I click "YES" because my app is published on Google Play

4.) After selecting an application from Google Play, we start creating ad unit. Press "NEXT: CREATE AD UNIT"

5.) Choose Banner, Press "SELECT"

6.) Enter "Ad unit name" and Press "CREATE AD UNIT"

7.) Copy you "app id" (1) to constant value "admob_app_id" and "ad unit ID" (2) to constant value "banner_ad_unit_id" in file "res/values/strings.xml", and press "DONE"

8.) Banner creation and configuration are complete. If the application uses Rewards Ads, continue: How to get ad_unit_id for Rewarded Ads from Admob?